The present invention relates to a shock absorbing material, and in particular relates to a shock absorbing material for automobiles, suitable for reducing head injury criteria by absorbing shock energy imparted to the heads of passengers in the car interior at the time of a crash.
As shock absorbing materials for automobiles, the followings have been proposed conventionally:
i) Japanese Unexamined Utility Model Publication No. 6-42437 discloses one comprising a pillar guard of a resin with a hollow shape, with a rigid polyurethane foam provided in a hollow part thereof for absorbing shock.
ii) Japanese Unexamined Patent Publication No. 8-2358 discloses a pad material comprising a foam material or a rubber material.
iii) Japanese Unexamined Patent Publication No. 8-72642 discloses one comprising a cushion member made from a rigid polyurethane foam covered with a shape-protecting material made of a sheet metal with a concave portion formed therein.
iv) Japanese Unexamined Patent Publication No. 6-211088 discloses a shock absorbing material mounted with a trim.
v) Japanese Unexamined Patent Publication No. 7-16867 discloses a shock absorbing material comprising a bead-like molded resin, with a large number of upright ribs provided on one side surface as shown in FIG. 9 described later.
vi) Japanese Unexamined Patent Publications Nos. 8-142234 and 8-295194 disclose a shock absorbing material made from a polyolefin resin material, with upright lattice-like ribs provided.
The above-mentioned conventional shock absorbing materials have the following disadvantages.
That disclosed in Japanese Unexamined Utility Model Publication No. 6-42437 uses a rigid polyurethane foam as the protecting material for shocks to the head; however, since it has a composite structure with a hollow-shaped resin part (trim), the compression stress of the rigid polyurethane foam must be as low as 0.2 to 2 kg/cm2, and thus the optimum structure utilizing the characteristics of the polyurethane foam cannot be provided. Moreover, since the irregular shape is for reducing the weight and maintaining strength thereof, but is not for improving the shock absorbing ability, the shock absorbing ability cannot be improved.
Japanese Unexamined Patent Publication No. 8-2358 describes an example of the conventional technique of a pad shock absorbing material comprising a foam material or a rubber material. This example mentions that the pad is elastically deformed, and thus it is not a rigid polyurethane foam. Moreover, regarding the concave shape, since the part contacting the car body is extremely thin, the pad must be thick in order to yield sufficient shock absorbing ability, and thus problems arise in that due to reduced car interior space in the automobile, comfort, convenience in entering and exiting, and visibility range are degraded.
That disclosed in Japanese Unexamined Patent Publication No. 8-72642 has an overall concave shock absorbing structure. However, the soft or rigid polyurethane foam itself used as the cushion material does not have an irregular shape to improve performance, but has a concave shape only at the mounting part. Moreover, it is mentioned that a sufficient shock absorbing ability cannot be achieved with an overall excessively high or low rigidity, but a specific numerical value or range is not described, and thus it is difficult to ensure that good shock absorbing ability can be obtained.
Since that disclosed in Japanese Unexamined Patent Publication No. 6-211088 is fastened onto a car body with trim by a clip, trim is necessary for mounting the shock absorbing material. Therefore, use thereof as a head protecting material is limited. For example, it is not suitable for side rails, or the like. Furthermore, the shock absorbing material does not have an irregular shape. Moreover, it is mentioned that it has a thickness necessary for absorbing shock, but specific thicknesses or hardnesses are not described, and thus it is difficult to ensure that good shock absorbing ability can be obtained.
If a force is applied to a face contact part locally, particularly by a spherical object such as the head of a dummy, the force is concentrated in the beam part between ribs, as disclosed in Japanese Unexamined Patent Publication No. 7-16867, comprising a bead-like molded resin, and thus sufficient shock absorbing ability cannot be obtained. If the shaped part is made of a rigid polyurethane foam, the beam part will break. As a result, a distance effective for absorbing energy cannot be obtained.
Those disclosed in Japanese Unexamined Patent Publication Nos. 8-142234 and 8-295194 have a thin lattice-like rib of 0.6 to 1.2 mm, and furthermore, it is disadvantageous in that because a polyolefin resin rib absorbs energy basically by the bending of the rib, shock absorbing ability is highly dependent on the direction of the shock.
As mentioned above, none of the conventional shock absorbing materials obtaining optimum shock absorbing ability by actively designing the shape of the shock absorbing material. As a result, it has never been possible to provide a high shock absorbing ability by the shock absorbing material itself.
On the other hand, since the thicknesses of pillars and side rail portions in an automobile greatly influences the comfort, styling, and security of the range of view in terms of safety, in order to protect passengers by reducing head injury criteria of the passengers without hindering these factors, a shock absorbing material capable of realizing sufficient shock absorbing ability, and which is a thin shock absorbing material, is needed.
In these days, in order to improve automobile safety, head protecting material for damping shocks to the head of a passenger has been mounted to a car body inner wall, a ceiling material, a trim, or the like.
The head protecting material, in general, is a strip-like member about 60 mmxc3x97450 mmxc3x9720 mm. Conventionally, those comprising a rigid polyurethane foam, those comprising a bead-like foamed member of a polypropylene, polyethylene or polyolefin resin, resin ribs of ABS, polypropylene, polyethylene, polyolefin, or the like, have been provided. These head protecting materials are made of a material with a relatively high hardness.
In mounting such a head protecting material to, for example, the rear surface of a ceiling material of an automobile, it is mounted along the sides of the ceiling material 10 corresponding to the seat position of passengers as shown in FIG. 13A as 11A, 1B, 1C, 11D. As shown in FIG. 13B (enlarged view of the cross-section taken on the line XIIIBxe2x80x94XIIIB of FIG. 13A), an adhesive tape 12 or an adhesive is used for mounting.
Conventionally, as the adhesive tape 12, one comprising a base material of non-woven fabric, paper, plastic film, or the like, and an adhesive material applied thereon for forming an-adhesive layer has been used. Moreover, as the adhesive, a hot melt adhesive, a solvent adhesive, or an aqueous adhesive has been used.
The conventional head protecting material mounting method involves the following problems.
Although the mounting operation itself can be easier by mounting with an adhesive tape compared with the case of using an adhesive, since the head protecting material is made of a relatively hard material and thus cannot follow the deformation of the mounted surface, the head protecting material can easily peel and fall off. That is, if the head protecting material is mounted to a part of a flat and wide area like the rear surface of the ceiling material, when the part is deformed by twisting during transportation, the adhesive surface peels and falls off due to inability to conform to the deformations of the hard head protecting material. Moreover, in assembling a part mounted with the head protecting material, such as the ceiling material with a car body, since the head protecting material projects from the part, such as the ceiling material for the thickness thereof as a level difference, when the projecting head protecting material contacts the car body, or the like, the head protecting material falls off from the part also in this case due to inability of the adhesive surface to follow the deformation for the hardness of the head protecting material.
On the other hand, in the case of mounting with an adhesive, since the part needs to be left for about one day after application of an adhesive in a method of using an aqueous adhesive, a long mounting operation time is required, and thus it is not practical.
Moreover, since the head protecting material needs to be fixed and held for 20 to 30 seconds after application when a hot melt adhesive is used, and an standing time is required after application of an adhesive in the case of a solvent adhesive, both require a large number of bonding steps, and thus are difficult to execute. Moreover, since both the hot melt adhesive and the solvent adhesive become adhesive by hardening and the adhered to surface becomes hard, the adhered to surface cannot conform to the deformation when there is deformation during transportation or a crash of the car body so that a problem arises in which the head protecting material falls off, as in the case of the adhesive tape.
Accordingly, a first object of the present invention is to provide a shock absorbing material for an automobile having extremely good shock absorbing ability and which is suitable for absorbing shock energy from a pillar impacting a head of a passenger including a driver in a cabin at the time of a crash of an automobile, or the like, and reducing head injury criteria.
A shock absorbing material according to the present invention consists of a rigid polyurethane foam having a 3 kg/cm2 or more compression stress, and has a shape of a board with concave parts arranged on at least one planar surface thereof.
In the shock absorbing material according to the present invention, stable shock absorbing ability can be achieved by absorbing shock energy by crushing of at least one wall part between the adjacent concave portions in the shock absorbing material, and by the crushed wall(s) entering into the concave portions successively. Furthermore, owing to the entrance of the crushed wall into the concave portions, a large stroke can be obtained, and thus the shock value to be applied to the passengers can be reduced sufficiently.
In the present invention, it is preferable that the ratio of the volume of the concave portions with respect to the total of the volume of the rigid polyurethane foam part and the volume of the concave portions (hereinafter the ratio may be referred to as the xe2x80x9cexcavated ratioxe2x80x9d) be 10 to 40%.
Moreover, it is preferable that the concave portions are arranged parallel in one direction, with an arrangement pitch of 30 mm or less, and that the width of the wall between the adjacent concave portions has a thickness of 2 to 15 mm.
The shock absorbing material of the present invention may be mounted to an automobile body or an interior part such as a head liner, a trim, or the like thereof as a protecting material against shocks to a head of a person in a cabin of the automobile.
A second object of the present invention is to provide a method for mounting a protecting material to a ceiling material, a trim, an automobile body, or the like easily and securely.
In a method for mounting a protecting material by attaching the protecting material in an automobile with an adhesive sheet according to the present invention, the adhesive sheet comprises a base material made of a foam material and an adhesive layer formed thereon.
With the adhesive sheet having a foam material as the base material, peeling off or falling off of the protecting material can be prevented due to deformation of the foam material provided as the base material.
In the present invention, it is preferable that the density of the foam material comprising the base material of the adhesive sheet is 0.005 to 0.5 g/cm3, and the base material thickness is 0.5 to 5 mm.